I took a quick walk through one of our restored wetlands last week. Most plants had finished blooming for the year, but in some recently-mowed patches, there were some scattered flowers of beggarticks (Bidens sp) and blue lobelia (Lobelia siphilitica). I knelt down to look more closely at some small bees I spotted crawling around on the lobelia flowers.
I saw one bee crawl in and out of one of the flowers, but for the most part, the bees (and a few flies) were all hanging around at the base of the flowers. As I watched, I saw one slide its long tongue into the flower. I couldn’t tell if it opened up a hole or just took advantage of one that was already there. Either way, it was apparently “stealing” nectar from the flower through a back window rather than entering politely through the front door.
I sent photos and questions to both Jennifer Hopwood and Mike Arduser, who are always generous about sharing their expertise with me. They both agreed with my interpretation, and Mike added some additional information. He said that blue lobelia flowers have slits in them that make this kind of nectar robbing pretty easy for bees.
It seems an odd strategy for a flower to make it easy for bees to steal nectar without providing any pollination services in return. Maybe the slits serve another purpose and the benefits outweigh the costs. Or maybe it’s just a random loophole that natural selection hasn’t yet closed. Regardless, blue lobelia plants tend to produce copious amounts of seed, so the flowers must get enough front door visitors to do the job.
In addition to the bees, there were a lot of flies hanging around the flowers too. Flies have pretty short tongues, and it didn’t look like any of them were sticking those tongues into the flower slits. Instead, they seemed to be feeding on the outside surface of the flower. Maybe nectar was seeping through those flower slits? Or maybe the bees were a little sloppy with their drinking and the bees were cleaning up after them? Whatever the reason, I saw at least as many flies as bees on the flowers, so there must have been some attraction.
I wish now that I’d spent more time examining the flowers, and that I’d brought one home with me so I could look at the slits under a scope. However, I hadn’t really planned to stop at the wetland, let alone to kneel down in the mud to look at bees stealing nectar from hapless flowers. Also, my neck was starting to throb a little from holding my head at an uncomfortable angle necessary to photograph the bees. Instead of sticking around to learn more, I took my camera, my muddy jeans, and my sore neck back to the truck and headed home.